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Abstract:

The present disclosure relates to an optical transceiver for use in
optical fiber communications and/or telecommunications systems and, more
specifically, a low power consumption, long range pluggable transceiver.
The transceiver generally comprises a photodiode with a transimpedance
amplifier (PIN-TIA); an electro-absorption modulated laser (EML); an
optical detector; and a directly modulated laser (DML) driving module
connected between the PIN-TIA and EML laser configured to drive the EML
laser. A low power-consumption DML driving module is utilized to drive
the EML laser, so as to further reduce power consumption. An impedance
matching circuit can be applied to modulate an electro-absorption (EA)
modulator of the EML laser with maximum efficiency.

Claims:

1. A transceiver comprising: a photodiode with a transimpedance
amplifier; an electro-absorption modulated (EML) laser; a bias current
control circuit configured to provide a bias current to the EML laser;
and a directly modulated laser (DML) driving module coupled between (i)
said photodiode and transimpedance amplifier and (ii) said EML laser,
said DML driving module configured to drive said EML laser.

2. The transceiver of claim 1 , wherein said EML laser is configured to
operate at a working temperature in one of two or more temperature
ranges, wherein each temperature range has a corresponding set value.

3. The transceiver of claim 2, further comprising a microcontroller or
microprocessor configured to: obtain a voltage of a thermal resistor in
the EML laser; determine an internal temperature of said EML laser;
determine a corresponding operating temperature range; set a
corresponding temperature value for said EML laser within said
corresponding operating temperature range; and/or maintain said internal
temperature of said EML laser within said corresponding operating
temperature range.

4. The transceiver of claim 3, wherein said microcontroller or
microprocessor is configured to utilize a
proportional-integral-derivative (PID) control loop such that said EML
laser operates at a predetermined temperature.

5. The transceiver of claim 1, further comprising a temperature control
circuit configured to cool and/or heat said EML laser.

6. The transceiver of claim 1, wherein said EML laser comprises an
electro-absorption (EA) modulator, and said transceiver further comprises
an impedance matching circuit configured to regulate the EA modulator.

7. The transceiver of claim 1, wherein said bias current control circuit
comprises a DC-DC converter and a filter network.

8. The transceiver of claim 3, wherein said microprocessor or
microcontroller obtains said voltage of said thermal resistor, and said
transceiver further comprises an analog-to-digital converter (ADC)
configured to provide a digital representation of said voltage to said
microprocessor or microcontroller.

9. The transceiver of claim 3, wherein said microprocessor or
microcontroller sets said corresponding temperature value for said EML
laser, and said transceiver further comprises using a temperature control
circuit configured to maintain said internal temperature of said EML
laser.

10. A transmitter comprising: an electro-absorption modulated (EML)
laser; a bias current control circuit configured to provide a bias
current to the EML laser; and a directly modulated laser (DML) driving
module configured to drive said EML laser.

11. The transmitter of claim 10, further comprising a temperature control
circuit configured to cool and/or heat said EML laser such that said EML
laser is substantially maintained at a predetermined temperature within
one of a plurality of non-overlapping temperature ranges.

12. The transmitter of claim 10, wherein said bias current control
circuit comprises a DC-DC converter and a filter network.

13. The transmitter of claim 10, further comprising a microcontroller or
microprocessor configured to: obtain a voltage of a thermal resistor in
the EML laser; determine an internal temperature of said EML laser;
determine a corresponding operating temperature range; set a
corresponding temperature value for said EML laser within said
corresponding operating temperature range; and/or maintain said internal
temperature of said EML laser within said corresponding operating
temperature range.

14. A method of operating an electro-absorption modulated (EML) laser,
the method comprising: (i) determining an internal temperature of said
EML laser; (ii) determining a corresponding operating temperature range
for the EML laser; (iii) setting a corresponding temperature value for
said EML laser within said corresponding operating temperature range;
and/or (v) maintaining said internal temperature of said EML laser within
said temperature range.

15. The method of claim 15, wherein said method detects said internal
temperature of said EML laser, and detecting said internal temperature of
said EML laser comprises determining a voltage of a thermal resistor in
said EML laser.

16. The method of claim 14, further comprising cooling said laser when
said internal temperature is greater than said corresponding temperature
value, and heating said EML laser when it is at a temperature lower than
said corresponding temperature value.

17. The method of claim 14, wherein said corresponding operating
temperature range comprises a first range of below 10.degree. C., a
second range of from 10.degree. C. to 30.degree. C., and a third range of
above 30.degree. C.

18. The method of claim 18, wherein said corresponding temperature value
is about 5.degree. C. in said first range, said corresponding temperature
value is about 20.degree. C. in said second range, and said corresponding
temperature value is about 40.degree. C. in said third range.

19. The method of claim 14, further comprising controlling a bias current
applied to said EML laser with a proportional-integral-derivative (PID)
algorithm.

Description:

FIELD OF THE INVENTION

[0001] The present invention generally relates to the field of
optoelectronic conversion devices (e.g., optical transceivers) in fiber
optic communications and telecommunications. More specifically,
embodiments of the present invention pertain to a long range, low power,
small form-factor pluggable (SFP+) transceiver, circuits and devices
therefor, and method(s) of using the same.

DISCUSSION OF THE BACKGROUND

[0002] As a core component of optical (e.g., fiber-optic) communications
networks, optical transceivers have provided optical data transmission
systems with low cost, large capacity, and low power consumption. Such
transceivers make fiber-optic networks more complete, smaller, and can
increase access to the transceiver interface board. Such transceivers
comprise optoelectronic component(s), functional circuitry, a laser and a
photodiode-transimpedance amplifier (PIN-TIA), in which the
optoelectronic component(s) include both transmitter and receiver
circuitry. In some embodiments, the transmitter circuitry comprises a
light-emitting diode (LED), a vertical-cavity surface-emitting laser
(VCSEL), Fabry-Perot circuitry (FP), and/or distributed feedback (DFB)
and electro-absorption modulated laser (EML) circuitry. Additionally, the
receiver circuitry can comprise a p-type/intrinsic/n-type photodetector
(e.g., a PIN photodiode) and/or an avalanche photodetector (APD).

[0003] Conventional high-capacity, long-range, high-speed transceivers
utilize a cooled EML laser and laser driver. However, such lasers and
drivers consume large amounts of power, thus making it difficult to
reduce power consumption. Additionally, with the high power consumption
required by temperature controllers available on today's market, such
controllers are especially inefficient for cooling devices under low
current conditions, thus increasing the power consumed by the entire
transceiver. For example, in an SFP+ transceiver (which are transceivers
configured to operate at speeds faster than those of SFP transceivers),
in which an EML laser driver is utilized to drive an EML laser, the EML
laser can consume large amounts of power.

[0004] In such a receiver, to ensure that the laser functions properly at
any given temperature within a given temperature range, the temperature
of the EML laser is set to a temperature (e.g., TEML) within a given
temperature range, and subsequently adjusted by cooling (if the laser is
at a higher temperature) or heating (if the laser is at a lower
temperature). The greater the temperature difference between TEML
and the given temperature, the greater the cooling or heating required to
obtain the temperature TEML, and thus, the more power consumed.

[0005] Additionally, in certain conventional embodiments, a direct current
(DC) from a MOS transistor (e.g., a MOSFET) is used as an input bias
current to the EML laser, and a current-limiting resistor (which itself
consumes power) is connected in series between the MOS and EML laser to
limit current. Furthermore, even when a voltage is directly supplied, it
can be difficult to reduce transceiver power consumption.

[0006] The technical solutions above are all causes of high power
consumption related to conventional SFP and SFP+ transceivers (i.e., SFP
transceivers capable of operating at high data rates), as well as other
similar optical transceivers which may benefit from low power consumption
solutions. The present invention overcomes the shortcomings of the
conventional technology, and provides a long reach, low power
consumption, pluggable transceiver configured to effectively reduce power
consumption.

SUMMARY OF THE INVENTION

[0007] Embodiments of the present invention relate to a low power
consumption, long range, pluggable (e.g., SFP+-compatible) transceiver
comprising a photodiode with a transimpedance amplifier (PIN-TIA); an
electro-absorption modulated (EML) laser; an optical detector; and a
directly modulated laser (DML) driver circuit (which may be implemented
as an integrated circuit) configured to drive the EML laser (e.g., for
low extinction ratio applications) and/or an EML laser driver (which may
also be implemented as an integrated circuit) configured to drive the EML
laser (e.g., for large extinction ratio applications). In one embodiment,
a low-power consumption DML laser driver circuit is used to drive the EML
laser to reduce power consumption. Typically, the DML laser driver
consumes about half of the power of the EML laser driver. Additionally,
in some embodiments, an impedance matching circuit is used to modulate an
electro-absorption (EA) modulator of the EML laser to maximize efficiency
when the output impedance of the DML laser driver circuit does not match
the input impedance of the EML laser. The DML laser driver circuit that
drives the EML laser is controlled via a microcontroller that may be
configured to adjust a cross point, control an output voltage amplitude
and/or a pre-emphasis function, and/or accurately drive the EML laser
(optionally, with maximum efficiency).

[0008] In another embodiment, and to further reduce power consumption, the
present EML laser can be configured to apply a semi-cooling method and
divide the working temperature of the EML laser into 2 or more ranges,
where each temperature range or EML laser chip temperature profile (or
group of settings) has a corresponding set or predetermined value or
range of values based on ambient temperature or the transceiver module
case temperature. Additionally, the present invention can include a
micro-controller configured to (i) obtain a voltage of a thermal resistor
in the EML laser via an analog-to-digital converter (ADC), (ii) detect an
internal temperature of the EML laser, (iii) determine a corresponding
operating temperature range for the EML laser, (iv) set a corresponding
temperature value within the operating temperature range for the EML
laser via a control circuit, and/or (v) limit the temperature of the EML
laser within the operating temperature range via the (temperature)
control circuit. The EML laser chip temperature settings or temperature
profile consists of a constant temperature setting and/or a linear
temperature relationship for a predetermined temperature range of the EML
laser. In commercial applications, transceivers with EML lasers generally
operate at a module case temperature in the range of -5° C. to
70° C. Thus, conventional transceivers' design requires heating at
lower temperatures and cooling at higher temperatures, and conventional
transceivers also always consume power since the EML laser chip
temperature is set to a constant temperature regardless of the
transceiver's operating temperature. For example, in such transceivers, a
fixed temperature T is set for the laser within the operational
temperature range of the transceiver, and the fixed temperature T is
maintained by cooling the EML laser when the EML laser is at a higher
operating temperature and heating the laser when it is at a lower
operating temperature. The greater the temperature difference, the
greater the cooling or heating required to reach the fixed temperature T,
and the more power consumed in doing so.

[0009] In the present invention, the laser semi-cooling method has been
utilized to adjust and/or tune the laser chip temperature setting range
to minimize power consumption. For example, a first temperature (e.g.,
T1), a second temperature (e.g., T2), and a third temperature (T3) can be
utilized, wherein T2 is the normal (standard operating) temperature, T1
is a lower temperature, and T3 is a higher temperature. When utilizing
several temperatures, the laser may function at temperature T1 when the
operating temperature decreases, and at temperature T3 when the operating
temperature increases, thereby reducing temperature variations and
differences, and reducing power consumption accordingly. That is,
temperature ranges are set using corresponding target temperatures closer
to the actual operating temperature, so as to reduce the amplitude of
temperature adjustment (if necessary), thereby reducing power
consumption. By utilizing temperatures T1, T2 and T3, different
temperature profiles can be utilized, such as a linear curve or an
exponential curve for the temperature fluctuations between temperatures
T1 and T2, temperatures T2 and T3, etc.

[0010] To ensure the EML laser functions at a set operating temperature, a
thermoelectric cooler (TEC) control circuit can be utilized. Currently,
there are several TEC control ICs commercially available, but these ICs
are designed for supplying a relatively large TEC current. For example,
for low power consumption applications (e.g., SFP+ transceivers), the
efficiency of these TEC control ICs is about 20%. However, the present
disclosure includes one or more DC/DC converters (or other similar
voltage controlled current sources) coupled to a TEC control circuit that
can be configured for different applications. For example, in certain
exemplary applications utilizing an SFP+ transceiver, the TEC control
circuit can include one or more DC/DC converters to achieve greater than
90% efficiency. The DC/DC converter-based TEC control circuit is
controlled by a proportional-integral-derivative (PID) algorithm that is
used to automatically adjust the operating temperature. Using an
auto-control principle, a PID control loop feeds back the operating
temperature obtained (e.g., measured) from the EML laser to a
microcontroller. The microcontroller then compares the actual operating
temperature with a preset target temperature and, to ensure that the two
temperatures are equal, makes an adjustment (if necessary) via a
temperature control circuit. The temperature control circuit controls the
cooling and heating of the EML laser (e.g., through a heat transfer
device) according to an output of the microcontroller, so as to approach
the fixed (preset or target operating) temperature, and maintain the
preset/target operational temperature. In one embodiment, to control the
cooling and heating current, dual DC/DC converters can be used for
simultaneously sourcing and sinking the current through microcontroller.

[0011] In the present invention, a pulse-width modulation (PWM) bias
current is utilized to generate a current that can be used to provide an
input bias current for the EML laser. Specifically, an output of a
microcontroller or microprocessor controls a
direct-current/direct-current (DC/DC) converter in the PWM bias circuit,
which provides one or more output signals having various duty ratios. The
output signals are then processed by a filter circuit to provide the bias
current to the EML laser.

[0012] In the present invention, a low power requirement DC/DC converter
may be used to directly provide an accurate, continuous current supply to
the EML laser. The DC/DC converter has high efficiency as a current
source for laser bias current. Compared to existing technology, the
present long reach transceiver has a low-power requirement and is able to
reduce power consumption and increase transceiver efficiency (precision).
These and other advantages of the present invention will become readily
apparent from the detailed description of various embodiments below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a diagram showing an exemplary transceiver according to
the present invention.

[0016]FIG. 3B shows a diagram illustrating a circuit 350 comprising a DML
laser driver IC configured to drive an EML laser, wherein an impedance
conversion circuit is used to match the output impedance of the DML laser
driver IC to the input impedance of the EML laser.

[0020] Reference will now be made in detail to various embodiments of the
invention, examples of which are illustrated in the accompanying
drawing(s). In order to achieve the objectives, technical solutions and
advantages of the present invention more clearly, further details of the
invention are described below with regard to the Figure(s). While the
invention will be described in conjunction with the following
embodiments, it will be understood that the descriptions are not intended
to limit the invention to these embodiments. On the contrary, the
invention is intended to cover alternatives, modifications and
equivalents that may be included within the spirit and scope of the
invention as defined by the appended claims. Furthermore, in the
following detailed description, numerous specific details are set forth
in order to provide a thorough understanding of the present invention.
However, it will be readily apparent to one skilled in the art that the
present invention may be practiced without these specific details. In
other instances, well-known methods, procedures, components, and circuits
have not been described in detail so as not to unnecessarily obscure
aspects of the present invention. The embodiments described here are only
used to explain, rather than limit, the invention.

[0021] For the sake of convenience and simplicity, the terms "connected
to," "coupled with," "coupled to," and "in communication with" (which
terms also refer to direct and/or indirect relationships between the
connected, coupled and/or communicating elements unless the context of
the term's use unambiguously indicates otherwise) are generally used
interchangeably herein, but are generally given their art-recognized
meanings

[0022] FIG. 1 illustrates an exemplary embodiment of a low power
consumption, long-range transceiver (e.g., a SFP+ transceiver) 100
comprising a receiver optical sub assembly (ROSA) 130. ROSA 130 comprises
a transimpedance amplifier (TIA) 135 and a photodiode (PD) (e.g., a
p-type intrinsic n-type [PIN] photodiode) 132. ROSA 130 (e.g., also
referred to as PIN-TIA 130) is configured to receive an optical input
signal IN (e.g., from the optical signal medium such as a fiber optic
cable) and provide an electrical output signal to limiting amplifier 140.
Limiting amplifier 140, in communication with electrical interface 160,
is configured to limit the voltage of the input signal, and provide an
amplified output signal to electrical interface 160. Electrical interface
160 is coupled to a microprocessor 150 via one or more buses, and
provides one or more signals (e.g., from an electrical component in
communication with transceiver 100) to microprocessor 150.
Microcontroller 150 is configured to control and/or regulate various
functions of the transceiver modules (e.g., thermo-electric cooler [TEC]
control circuit 180, directly modulated laser [DML] driver circuit
[module] 170, TWM laser bias current control circuit 110, etc.).

[0024] Furthermore, transceiver 100 comprises a PWM bias current control
circuit 110, which is used for laser bias current generation with
low-power consumption. The PWM bias current circuit is achieved through a
DC/DC converter with high efficiency for desired laser bias current for
EML laser 120. As shown, DML driver circuit 170 is connected between
electrical interface 160 and EML laser 120. As illustrated, DML laser
driver IC 170, rather than an EML laser driver IC, is used to drive the
EML laser 120 so as to effectively reduce power consumption.

[0025] Microprocessor/microcontroller 150 maintains a desired or
predetermined optical output power (e.g., signal OUT provided by EML
laser 120) by controlling the PWM laser bias current control circuit 110
which generates the laser bias current on the DFB-LD section 125 of the
EML laser 120. The electrical data signal comes from electrical interface
160 and is amplified by DML laser driver circuit 170, wherein the
amplification or modulation amplitude is controlled by
microprocessor/microcontroller 150. The amplified electrical data signal
is applied to EA modulator 122 of EML laser 120 to achieve the optical
output signal OUT. Additionally, microcontroller 150 adjusts and
maintains the eye diagram (e.g., the eye crossing point, extinction
ratio, etc.) of the output optical signal OUT by controlling the DML
laser driver circuit 170. Furthermore, temperature control of the EML
laser 120 (e.g., DFB-LD section 125) is maintained through a TEC control
closed feedback loop. Specifically, microcontroller 150 uses
analog-to-digital converter (ADC) 145 to monitor the temperature of the
EML laser 120 (e.g., the DFB-LD 125 of EML laser 120). Microcontroller
150 then processes (e.g., compares) the temperature data with a
predetermined or desired temperature setting through a PID
(Proportional-Integral-Derivative) algorithm to provide the temperature
difference data (e.g., via the closed feedback loop) to TEC control
circuit 180 and generate the TEC cooling or heating current for EML laser
120. Incoming optical data signal IN goes into ROSA 130, which converts
the optical signal IN to an electrical signal, which enters the
electrical interface 160 after amplification by limiting amplifier 140.

[0026] The present EML laser applies a semi-cooling method. Most optical
transceivers operate within one of three temperature ranges, depending on
the application and/or environment (e.g., commercial, extended, or
industrial) in which they are used. In a first temperature range for
commercial applications, optical transceivers generally should operate in
a temperature range of from about -5° C. to about 70° C.
Additionally, for extended applications, optical transceivers generally
should operate in a second temperature range of from about -5° C.
to about 85° C., and for industrial applications, optical
transceivers generally should operate in a third temperature range of
from about -40° C. to about 85° C. For example, in
commercial applications, the present EML laser chip temperature can be
configured to operate within a temperature range of about 25° C.
to 60° C., such as 25° C. (e.g., T1), 45° C. (e.g.,
T2), and 55° C. (e.g., T3) based on different ambient temperature
or transceiver case temperature determinations. The present laser chip
temperature setting adjustments minimize the difference between the laser
chip temperature and the ambient temperature, thereby minimizing TEC
power consumption. The EML laser of the present invention may operate at
25° C. when the transceiver module case temperature is
comparatively low (e.g., a temperature under 25° C.), at
35° C. when the transceiver module case temperature reaches a
temperature between 25° C. and about 55° C., and at
45° C. when the transceiver module case temperature is
comparatively high (e.g., a temperature above 55° C.). The laser
chip temperature can be controlled (e.g., linearly increased or
decreased) using the microcontroller between T1 and T3. By utilizing the
present transceiver, temperature variations between the actual operating
temperature and the preset (target) operating temperature are reduced,
and less power is consumed in heating and cooling the EML laser.

[0027]FIG. 2 shows an exemplary laser chip temperature setting profile
under industry-standard operating temperature conditions. As shown in the
graph 200 of FIG. 2, when the temperature of the transceiver (TRx) module
case (shown in ° C.) increases to a transceiver case temperature
B, the laser chip temperature (also shown in ° C.) is linearly
increased by the microcontroller until reaching a temperature A. For a
given operating range of TRx case temperatures (e.g., between
temperatures B and D), the laser chip temperature remains at a constant
value (e.g., temperature A). In some embodiments, the given range of TRx
case temperatures where the laser chip temperature remains constant is
from about between 35° C. to 75° C. Thus, the laser chip
temperature can be tuned and/or adjusted by the microcontroller with
respect to TRx case temperatures between temperature B and temperature D.
Additionally, for TRx case temperatures greater than temperature D, the
laser chip temperature can be adjusted by the microcontroller and
increased linearly. Thus, with a higher TRx case temperature range, a
smaller cooling current can be applied since the laser chip temperature
setting increases as the TRx case temperature increases. Similarly, for
TRx case temperatures less than temperature B, less heating current can
be applied since the laser chip temperature setting decreases as the TRx
case temperature decreases.

[0028] A PWM bias current control circuit 110 is utilized in the present
invention to generate an input bias current for the EML laser 120. The
PWM bias current control circuit 110 may comprise a DC/DC converter, a
filter network, and optionally, a digital-to-analog converter (DAC; e.g.,
DAC 503 in FIG. 5) at an input of the DC/DC converter. An output signal
of the microcontroller 110 controls the DC/DC converter of the PWM bias
circuit 110, which provides output signals having different duty ratios
(i.e., duty cycles) to the PWM bias circuit. The output signals are then
processed by the filter network (circuit) to provide a bias current to
the EML laser 120.

[0029] FIG. 3A illustrates an impedance matching circuit 300, by which the
impedance of a DML laser driver 310 (e.g., DML laser driver circuit 170
in FIG. 1) and the EML laser 320 can be matched. For example, in one
embodiment, the DML laser driver 310 in FIG. 3A (which can be implemented
as an IC) has a 25 ohm (Ω) output impedance, and the EML laser 320
has a 50 ohm (Ω) input impedance. However, the different impedances
can be matched in the circuit 300. In embodiments using or requiring a
large optical extinction ratio, an EML laser driver can be used instead
of the DML laser driver 310, although power consumption generally
increases. By matching the input impedance of the EML laser 320 with the
output impedance of the DML laser driver 210, power transfer can be
maximized and power consumption minimized.

[0030] As shown in circuit 300 of FIG. 3A, DML laser driver 310 is itself
a biasing circuit. Specifically, DML laser driver 310 comprises
resistances (e.g., resistors) 301 and 303, transistors 305 and 307, and
current source 309. Resistance 301 is coupled to a voltage source (e.g.,
Vcc), and to the collector of a first transistor (e.g., BJT 305) of
the DML laser driver 310 at node 302. Similarly, resistance 303 is
coupled to the voltage source and to the collector of a second transistor
(e.g., BJT 307) of the DML laser driver 310 at node 304. As shown,
current source 309 is coupled to the emitter of first transistor 305 and
to the emitter of second transistor 307, as well as a ground potential
(e.g., a potential of about 0V). In an alternative embodiment, first and
second transistors 305 and 307 are MOSFETs. Additionally, in certain
embodiments, resistances 301 and 303 have the same resistance value, as
do resistances 311 and 313, although one or both of these pairs of
resistances can have different values. Additionally, first transistor 305
is coupled to resistance 311 and capacitance (e.g., a capacitor) 312 at
node 302. Resistance 311 is coupled to a first power supply (e.g.,
Vcc), and (along with resistance 301 and BJT 305) is intended to
provide a predetermined impedance at node 302 that matches the impedance
at the input of EML laser 320. Capacitance 312 is also coupled to EML
laser 320. As shown, EML laser 320 comprises a resistance 321 and an EML
laser diode 322.

[0031] Second transistor 307 is coupled to a resistance 313 and a
capacitance 314 at node 304. Resistance 315, coupled to capacitance 314,
is also coupled to a ground potential (e.g., a voltage source of about
0V). Resistance 313 is coupled to the first power supply (e.g., Vcc)
and (along with resistance 303 and BJT 307) is intended to provide a
predetermined impedance at node 304. The equivalent output impedance from
laser driver 310 comprises resistors 301 and 311, and resistors 303 and
313. Thus, by optimizing the resistance of resistors 311 and 313, the
output impedance from the laser driver can be matched to the input
impedance of EML laser 320. Similarly, the conductive pathway (e.g., the
bus, wire, transmission line, etc.) between laser driver 310 and EML
laser 320 is designed to have an impedance value the same as or similar
to that of the input impedance of EML laser 321.

[0032] As shown in FIG. 3B, an alternative circuit 350 is provided by
which the output impedance of DML laser driver 310 is substantially
matched to the input impedance of EML laser 320. As discussed above with
respect to FIG. 3A, DML laser driver 310 comprises a biasing circuit,
itself comprising resistances 301 and 303, transistors (e.g., bipolar
junction transistors [BJTs]) 305 and 307, and current source 309. As
shown, resistances 301 and 303 are coupled to a voltage source Vcc,
and current source 309 is coupled to a ground potential (e.g., a voltage
source of about 0V).

[0033] Similar to circuit 300 of FIG. 3A, DML laser driver 310 in FIG. 3B
is coupled to capacitance (e.g., a capacitor) 312 at node 306, itself
coupled to EML laser 320. Capacitance 312 is also coupled to a resistance
319, itself coupled to a ground potential (e.g., a voltage of about 0V).
Furthermore, as discussed above, EML laser 320 comprises EML laser diode
322 and resistance 321 (e.g., arranged in a parallel circuit
configuration). Although there may be different laser packaging
configurations suitable for the present EML laser 320, in some
embodiments, resistor 321 has a resistance value of about 50 ohms and is
arranged in parallel with EML laser diode 322 (inside the EML laser 320).
The input impedance of EML laser 320 may be about 50 ohms, which may be
different from the output impedance of laser driver 310. Node 308 in DML
laser driver 310 is coupled to a capacitance (e.g., a capacitor 314),
which has its complementary plate coupled to relatively fixed potential
(e.g., resistance 317 coupled to a ground terminal). The resistance of
resistor 319 is configured to be similar to that of the EML laser 320, to
configure the input impedance of EML laser 320 as desired. Thus, by
optimizing the resistance of resistor 319, the equivalent input impedance
of EML laser 320 can be matched to the output impedance of laser driver
310. Additionally, the impedance of the conductive pathway (e.g.,
transmission line) between EML laser 320 and laser driver 310 has an
impedance value that is the same as or similar to that of the equivalent
input impedance of EML laser 320.

[0034]FIG. 4A shows a high-efficiency TEC control loop/circuit 400 that
utilizes dual DC-DC converters. As shown, circuit 400 comprises
microcontroller circuitry 410 comprising a first digital-to-analog
converter (DAC) 411, a second digital-to-analog converter (DAC) 415, a
microcontroller unit (MCU) 413, and an analog-to-digital converter (ADC)
417. As shown, first and second DACs 411 and 415 are configured by the
MCU 413 to provide analog signals to control or regulate DC-DC converter
block 420 such that a thermoelectric control (TEC) circuit 435 can
control sourcing or sinking a current that heats or cools the EML laser
(e.g., EML TOSA) 430.

[0035] Specifically, DC-DC converter block 420 is controlled by the DAC
415 and configured to source or sink a current that is used for TEC
control (e.g., the current that is provided to TEC circuit 435). DC-DC
converter 421 is configured to receive an analog DC signal (e.g., an
analog control signal) from first DAC 411 and output a source current or
a sink current (e.g., a TEC control current) for TEC control of the laser
(e.g., EML TOSA) 430. Additionally, DC-DC converter 423 is configured to
receive an analog DC signal (e.g., an analog control signal) from second
DAC 415 and output a source current or a sink current that is provided to
TEC circuit 435 such that TEC circuit 435 controls or regulates a
temperature of the EML TOSA 430. Depending on whether the operating
temperature of the laser chip 431 is to be increased or decreased, a
cooling current or a heating current is provided to TEC circuit 435.
Depending on the direction of the current flow provided by DC-DC
converter block 420, either the heating current or the cooling current is
provided. For example, when a current is provided that flows from DC/DC
converter 421 (which sources the current) through the TEC circuit 435 and
back to DC/DC converter 423 (which sinks the current), DC-DC converter
block 420 provides a TEC cooling current. Additionally, when a current is
provided that flows from DC/DC converter 423 (which sources the current)
through the TEC and then back to DC/DC converter 421 (which sinks the
current), DC-DC convert block 420 provides a TEC heating current.
Regulation of the current flow is provided via MCU 413. That is, MCU 413
monitors and/or regulates the operating temperature of laser chip 431 by
comparing the temperature of laser chip 431 to a predetermined laser chip
temperature setting, and determining if a cooling current or a heating
current is to be provided to the TEC circuit 435. For example, if MCU 413
determines that the operating temperature of laser chip 431 is too high
and a cooling current should be applied, MCU 413 sends a signal (e.g., a
control signal) to the DC/DC converter 421 to source the current flowing
through TEC circuit 435 and also sends a signal (e.g., a control signal)
to the DC/DC converter 423 to sink the current flowing through TEC 435
via first DAC 411 and second DAC 415, respectively.

[0036] As shown, circuit 400 comprises EML laser or EML TOSA 430,
comprising laser chip 431, thermistor 433, and TEC circuit 435. Laser
chip 431 may be implemented as a diode laser, on an integrated circuit
(e.g., a stand-alone IC or integrated with one or more other functions of
EML TOSA 430). Thermistor 433 is coupled to laser chip 431 such that a
change in the temperature of laser chip 431 corresponds to a change in
the resistance of thermistor 433. By utilizing such a configuration, the
resistance of thermistor 433 correlates to the temperature of laser chip
431. In one example, an increase in the temperature of laser chip 431
correlates to an increase in the resistance of thermistor 433.

[0037] As shown, TEC circuit 435 provides an analog signal to ADC 417
indicative of a temperature of laser 431. ADC 417 converts the analog
signal to a digital signal, which is then processed by MCU 413. Depending
on whether the temperature of laser chip 431 is to be increased or
decreased, MCU 413 provides a signal to either or both of first DAC 411
and second DAC 415. For example, when MCU 413 determines that the laser
temperature is to be increased, MCU 413 may provide a signal to first DAC
411, which is then provided to first DC-DC converter 421, and
subsequently to TEC 435 as temperature control signal 422, and when MCU
413 determines that the laser temperature is to be decreased, MCU 413
provides a signal to second DAC 415, which is then provided to second
DC-DC converter 423, and subsequently to TEC 435 as temperature control
signal 424. Alternatively, DC-DC converter block 420 can output a
differential signal on bus 422/424 that increases or decreases the
temperature of the laser 431 based on whether the voltage difference
across bus 422/424 is positive or negative. As a result, by utilizing the
present circuit 400, the laser temperature can be efficiently increased
or decreased to minimize temperature-dependent performance fluctuations
of the laser 431.

[0038] FIG. 4B illustrates a second exemplary TEC control loop or circuit
450 utilizing a single DC-DC converter 470. Circuit 450 comprises
microcontroller circuitry 410 (as discussed above with respect to FIG.
4A), coupled to a plurality of transistors (e.g., MOSFETs) 491, 493, 495,
and 497. As shown, MOSFETs 491 and 493 are p-channel, and MOSFETs 495 and
497 are n-channel. The source terminals of n-channel MOSFETS 495 and 497
are coupled to a ground potential (e.g., a potential of about 0V). Thus,
MOSFETs 491, 493, 495 and 497 are configured as switches, controlled by
the output of DAC 415 which can function to control the direction of
current flow, and thus, provide TEC heating and cooling functions.
Additionally, DC-DC converter 470 in FIG. 4B is configured to receive a
first voltage (e.g., Vcc) and provide a second voltage to the source
terminals of p-channel MOSFETs 491 and 493. The second voltage is one
that is suitable for thermoelectric control of EML laser 430. Thus, the
TEC control circuit 450 comprising DC-DC converter 470 and MOSFETs 491,
493, 495 and 497 can be a further example of the TEC control circuit
shown in FIG. 1.

[0039] As discussed above with respect to FIG. 4A, EML laser 430 comprises
TEC 435, laser 431, and thermistor 433, and is configured to provide an
analog signal to ADC 417 indicative of a temperature of laser 431. ADC
417 converts the received analog signal to a digital signal, which is
then processed by MCU 413. EML laser 430 and microcontroller 410
(including ADC 417) operate in the same way as FIG. 1 to effect or
provide feedback to the TEC control circuit, depending on whether the
temperature of laser 431 is to be increased or decreased, although the
configuration of FIG. 4B is particularly advantageous when the outputs of
DACs 411 and 415 provide a differential control signal (e.g., via signals
494 and 498) to TEC circuit 435.

[0040] FIG. 5 illustrates a low power consumption laser bias current
generation circuit 500 comprising a DC-DC converter 520 (e.g., similar to
DC-DC converter 470 in FIG. 4B). As shown in FIG. 5, the present bias
current generation circuit comprises microcontroller circuitry 510,
comprising MCU 413 (discussed above with respect to FIG. 4A) and
digital-to-analog (DAC) 503 (e.g., similar to DAC 411 of FIGS. 4A-B). As
shown, microcontroller circuitry 510 is configured to provide an analog
signal to DC-DC converter 520, which receives a voltage Vcc from an
external voltage source (not shown). DC-DC converter 520 is configured to
provide a DC signal to transistor (e.g., a p-channel MOSFET) 530.
Transistor 530 is also configured to receive a transmitter enable signal
at 501. For example, when enable signal has a first state (e.g., a
voltage of about 0V), the drain terminal of transistor 530 provides the
output of DC-DC converter 520 to the laser diode 540. However, when the
enable signal has a second state (e.g., a voltage of about Vcc), the
drain terminal of transistor 530 is at a high impedance state. Thus, the
transmitter is not enabled when the enable signal has the second state.

CONCLUSION/SUMMARY

[0041] The present disclosure relates to an optoelectronic conversion
device in an optical fiber communications and/or telecommunications
systems and, more specifically, a long range pluggable transceiver
configured to operate at a low power.

[0042] The foregoing descriptions of specific embodiments of the present
invention have been presented for purposes of illustration and
description. They are not intended to be exhaustive or to limit the
invention to the precise forms disclosed, and obviously many
modifications and variations are possible in light of the above teaching.
The embodiments were chosen and described in order to best explain the
principles of the invention and its practical application, to thereby
enable others skilled in the art to best utilize the invention and
various embodiments with various modifications as are suited to the
particular use contemplated. It is intended that the scope of the
invention be defined by the Claims appended hereto and their equivalents.